This invention relates generally to an apparatus for detecting voids in a conductive fluid. The present invention was developed specifically to detect voids in liquid sodium in conjunction with safety tests as part of the national Liquid Metal Fast Breeder Reactor safety development program, but is applicable to detect voids in any conductive fluid. Although there are numerous void detection devices available, various contraints of the sodium loop required a fresh approach. For example, the extremely limited space available eliminated most existing devices including ultrasonics. The pulsed-radiation environment eliminated gramma-ray and neutron attenuation methods. Internal probes could not be used because of the limited access to the sodium volume. And, the heavy-wall pipe would shunt electrical currents injected into the sodium via the electrical conductivity method.
The principle of operation of the present invention is based on inducing eddy currents in a conductive fluid by an external alternating-current magnetic field. Eddy currents, or more precisely, magnetic flux coupling, is the principle behind the eddy current flowmeter which is used to measure velocity of a conductive fluid. However, since an effective void detector must be insensitive to flow rate, the present invention bears little resemblance to a flowmeter.
Therefore, it is an object of the present invention to provide a void detector that can be used within the space limitations of a sodium loop.
It is another object of the present invention to provide a void detector that is insensitive to flow rates of the conductive fluid.
It is yet another object of the present invention to provide a void detector that can be used in a pulsed-radiation environment.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention.